High performance resilient skate wheel with compression modulus gradient

ABSTRACT

A high performance resilient skate wheel ( 100 ) including a solid core tire ( 102 ) and a hub ( 104 ) defining a bearing axis. The solid core tire ( 102 ) includes an inner ring ( 106 ) and an outer tire material ( 108 ) disposed about the inner ring and forming a rolling surface of the wheel. The outer tire material ( 108 ) is harder than the inner ring ( 106 ). The inner ring ( 106 ) has a stepped profile in cross section, defining a middle portion disposed axially between lateral portions of the inner ring, with the middle portion having a greater outer diameter than the lateral portions. Making the solid core skate wheel ( 100 ) includes providing a hub assembly having an inner ring ( 106 ) with a stepped profile in cross section disposed about a wheel hub ( 104 ), and over molding the inner ring with a tire material ( 108 ) forming a rolling surface of the wheel.

TECHNICAL FIELD

This invention relates to multi-layer skate wheels with a compression modulus gradient along the bearing axis of the wheel.

BACKGROUND

Many skate wheels, including skate wheels used in skateboards, inline skates, quad roller skates, street luges, and scooters, have a urethane or polyurethane tire bonded to the hub. Wheel size, wheel durometer or hardness, and wheel profile can be selected based on intended use (e.g., indoor or outdoor, hockey or speed skating, sport, recreational, transportation, or racing). For example, a wheel with a higher durometer (i.e., a harder wheel) and high resilience is faster and lasts longer but provides a rougher ride and less grip on the skating surface. A wheel with a lower durometer (i.e., a softer wheel), rolls more slowly but provides a smoother ride and better cornering grip.

Some skate wheels have been designed to offer a combination of skating characteristics. For example, U.S. Pat. Nos. 5,829,757 and 6,260,861 to Chiang et al., both of which are incorporated by reference herein, describe in-line skate wheels with a braking portion including a high-friction surface material and a skating portion including a low-friction surface material. The skating portion includes a higher proportion of low-friction surface material than the breaking portion. The wheels deliver variable fraction on skating surfaces in response to the angle of wheel contact with the ground, without sacrificing a smooth ride or wheel durability.

U.S. Pat. No. 6,227,622 to Roderick et al., which is incorporated by reference herein, describes a multi-layer skate wheel with a hub, a tire circumscribing the hub, and at least one layer or ring between the hub and the tire. The ring, constructed of an elastomeric material softer than the tire, is disposed at least partially between the hub and the tire. The wheel provides damping to counter rough road surfaces by the skater and allows increased grip of the skate wheel on the skating surface.

U.S. Patent No. 6,036,278 to Boyer describes a multi-durometer wheel for in-line skates. The wheels include a hub, with at least two cores of resilient material disposed coaxially about the hub, with the outer surface of a first core adapted for rolling over a surface, and at least one other core disposed within the first core. The relative hardness of the first core facilitates the rolling motion of the wheel over a surface and the relative softness of at least one other core facilitates the absorption of energy by the wheel during rolling motion of the wheel.

SUMMARY

In one aspect, a high performance resilient skate wheel includes a solid core tire and a hub defining a bearing axis. The solid core tire includes a multi-layer composite forming a ring around the hub coaxial with the bearing axis and surrounded at least in part by tire material fixed to the hub. The multi-layer composite includes a medial layer and at least two lateral layers adjacent to the medial layer. A hardness of the medial layer is equal to or greater than a hardness of at least one of the lateral layers, and a hardness of the tire material is greater than the hardness of at least one of the lateral layers. An outer diameter of the multi-layer composite is less than or equal to an outer diameter of the tire material. The wheel has a compression modulus gradient corresponding to the position of the multi-layer composite along the bearing axis of the wheel.

In another aspect, a wheel, such as an inline hockey or speed skating wheel, includes a hub defining a bearing axis and a tire mounted about the hub. The tire includes an inner ring and an outer tire material disposed about the inner ring. The outer tire material is harder than the inner ring and forms a rolling surface of the wheel. The inner ring has a stepped profile in cross section, defining a middle portion disposed axially between lateral portions of the inner ring, with the middle portion having a greater outer diameter than the lateral portions.

In another aspect, making a solid core skate wheel includes providing a hub assembly including a multi-layer composite in the shape of a ring disposed about a wheel hub, and over molding the multi-layer composite with a tire material such that the multi-layer composite is encapsulated or at least partially surrounded by the tire material. The tire material is fixed to the hub. The multi-layer composite includes a medial layer and two lateral layers adjacent to the medial layer. The hardness of the medial layer is equal to or greater than a hardness of at least one of the lateral layers. The hardness of the tire material is greater than the hardness of at least one of the lateral layers of the multi-layer composite.

In another aspect, making a solid core skate wheel includes providing a hub assembly having an inner ring disposed about a wheel hub, the inner ring having a stepped profile in cross section, defining a middle portion disposed axially between lateral portions of the inner ring, with the middle portion having a greater outer diameter than the lateral portions. The inner ring is over molded with a tire material forming a rolling surface of the wheel, such that the inner ring is encapsulated or at least partially surrounded by the tire material and the tire material is fixed to the hub, thereby forming a tire from the tire material having a hardness greater than the hardness of the inner ring.

Certain implementations can include one or more or the following features. The multi-layer composite or inner ring can be in contact with the hub or spaced from the hub, such as by the tire material. The multi-layer composite can include an even number of layers or an odd number of layers. In some cases, the Bashore rebound of the medial layer and the two lateral layers is at least about 65%, at least about 70%, at least about 75%, or at least about 80%. The Bashore rebound of the wheel can be at least about 65%, preferably at least about 70%, at least about 75%, or even at least about 80%. The tire material can be in contact with the hub. The tire material can have a hardness of between about 70 Shore A and about 95 Shore A. The hardness of the inner ring or the lateral layers of the multi-layer composite may be between about 40 Shore A and 75 Shore A, and a hardness of the medial layer may be between about 55 Shore A and 95 Shore A.

In some cases, the multi-layer composite has a compression stress between about 35 psi and about 160 psi when the compression strain is 20%. In certain cases, the multi-layer composite or the inner ring has a compression strain between about 5% and about 50% when the compression stress is 75 psi and/or a compression strain between about 8% and 40% at a compression stress of 50 psi. The compression modulus of the wheel proximate the medial layer is preferably greater than or equal to the compression modulus of the wheel proximate at least one of the lateral layers of the multi-layer composite over a range of 0% to 50% compression strain. The wheel may exhibit a compression modulus gradient corresponding to the position of the multi-layer composite along the bearing axis of the wheel, or a compression modulus gradient in which the compression modulus of the wheel varies along the bearing axis in accordance with the stepped profile of the inner ring.

In some cases, an inner diameter of the multi-layer composite or inner ring is between about 25 mm and about 120 mm. An outer diameter of the wheel can be between about 50 mm and about 120 mm. In some cases, a cross-section through a diameter of the wheel exposes a portion of the medial layer of the multi-layer composite with a length between about 6 mm and about 15 mm and a width between about 2 mm and about 8 mm. In certain cases, a cross-section through a diameter of the wheel exposes a portion of one of the lateral layers of the multi-layer composite with a length between about 2 mm and about 12 mm and a width between about 2 mm and about 8 mm.

The multi-layer composite or inner ring can include natural rubber, synthetic rubber, or a combination thereof. In some cases, the medial layer of the multi-layer composite includes thermoset urethane with a resilience of at least about 65%. In certain cases, the medial layer of the multi-layer composite includes natural rubber or neoprene rubber with a resilience of at least about 70%.

The multi-layer composite or inner ring can be formed by thermoset urethane casting of urethane precursors including one or more components such as MDI, TDI, PPDI; PTMEG with a molecular weight between about 1000 and about 3000; polydiol or polyamine, and butadiene diol, propylene diol, pentane diol, and hexanediol with a molecular weight between about 40 and about 80. The multi-layer composite can be formed by a process including B-stage curing of layers to form a multi-layer sheet or a process including adhering layers with an adhesive to form a multi-layer sheet, followed by die cutting of the multi-layer sheet to form rings of a multi-layer composite. In some cases, ring-shaped multi-layer composites can be formed by laminating ring-shaped layers together with an adhesive or a process including two-step casting in a partitioned mold. In some other cases, inner rings with stepped outer profiles can be formed as unitary, seamless masses of resin, such as in a casting process.

The wheel described herein is suitable for use as an in-line hockey skate wheel, an in-line speed skate wheel, a skateboard wheel, a scooter wheel, and the like. The compression modulus gradient results in a compression strain gradient under the weight of the user. This compression strain gradient provides a low rolling resistance for higher speed during rolling and increases grip for acceleration, cornering, and stopping. The increased grip may be attributed at least in part to the increased wheel conformance to (and thus an increased contact area with) the skating surface. The inner ring or multi-layer composite can also provide damping to reduce vibration amplitude and frequency from rough surfaces, resulting in a more comfortable ride.

The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a solid core skate wheel.

FIG. 2 is cross-sectional view of the skate wheel in FIG. 1.

FIG. 3 is a cross-sectional view of a skate wheel with an inner multi-layer composite having an odd number of layers and an asymmetrical cross section.

FIG. 4 is a cross-sectional view of a skate wheel with an inner multi-layer composite including an even number of layers.

FIGS. 5A-5F show partial cross-sectional views of skate wheels with inner multi-layer composites in contact with the hub and partially surrounded by tire material.

FIGS. 6A-6F show partial cross-sectional views of skate wheels with inner multi-layer composites surrounded by tire material.

FIGS. 7A-7D illustrate compression modulus gradients corresponding to the profile of a skate wheel along the bearing axis of the wheel, from one side of the inner multi-layer composite to the other side.

FIG. 8 illustrates of a multi-layer material suitable for use in a skate wheel.

FIG. 9 illustrates a ring-shaped multi-layer composite.

FIG. 10A illustrates an open casting mold for forming multi-layer composites for multi-layer skate wheels.

FIG. 10B illustrates a composite tube formed by the mold of FIG. 9A.

FIG. 11 is a plot of stress vs. percent strain for urethane rubber materials suitable for forming composite layers for inner multi-layer composites for a skate wheel.

DETAILED DESCRIPTION

FIG. 1 is a side view of multi-layer skate wheel 100 with solid core tire 102 fixed to hub 104. As used herein, a “solid core” tire refers to a non-pneumatic or semi-pneumatic tire that supports rolling loads by tire material compression rather than by a pressurized cavity.

FIG. 2 is a cross-sectional view of multi-layer skate wheel 100 in FIG. 1 along d-d (i.e. through the bearing axis of the wheel), with solid core tire 102 fixed to hub 104. Solid core tire 102 includes multi-layer composite 106 coaxial with hub 104, and surrounded at least in part by tire material 108. Multi-layer composite 106 includes three or more layers or a seamless mass of resin made of one or more materials, selected such that multi-layer skate wheel has a compression modulus gradient along the bearing axis a (i.e., the compression modulus varies along the bearing axis of the wheel). The compression modulus gradient along the bearing axis a may be symmetrical or asymmetrical about center line c of multi-layer skate wheel 100.

In some cases, multi-layer composite 106 includes a symmetrical arrangement of layers about center line c. In the example shown in FIG. 2, multi-layer composite 106 is a three-layer composite, with medial layer 110 and lateral layers 112 and 112′ adjacent to the medial layer. Medial layer 110 may be centered in the tire material 108 about center line c. Medial layer 110 is formed of a material with a hardness or compression modulus that is substantially equal to or greater than the hardness or compression modulus of lateral layers 112 and 112′, such that the compression modulus of wheel 100 is higher in the center of the wheel and decreases in both directions from the center along the bearing axis a.

Each layer of multi-layer composite 106 is a ring having an inner diameter id (shown for medial layer 110 in FIG. 2) substantially equal to or greater than the outer diameter of hub 104 proximate the layer of the multi-layer composite as positioned in the finished wheel. An outer diameter od of each layer of multi-layer composite 106 (shown for medial layer 110 in FIG. 2) is less than the outer diameter of tire material 108 proximate the layer of the multi-layer composite. As used herein, “outer diameter” means twice the maximum radial dimension of an element, as measured radially from the longitudinal axis a of the hub. Similarly, “inner diameter” means twice the minimum radial dimension of an element, as measured radially from the longitudinal hub axis. Viewed in cross section, portions of the layers of multi-layer composite 106 along a diameter of the ring may be thought of as aligned perpendicular to bearing axis a, with each layer having cross-sectional dimensions characterized by a width (or thickness) w and length (or height) l, as shown for medial layer 110 in FIG. 2. Width w and length l can be substantially the same or different for one or more layers of multi-layer composite 106. In some cases, a portion of one or more layers of multi-layer composite 106 contacts hub 104. In other cases, multi-layer composite is encapsulated or completely surrounded by tire material 108 and does not contact hub 104.

Multi-layer composites 106 are sized for use in a variety of skate wheels, with outer wheel diameters ranging from about 25 mm to about 120 mm in standard sizes such as 28 mm, 47 mm, 54 mm, 69 mm, 72 mm, 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, and 120mm, as well as additional non-standard sizes. In some cases, medial layer 110 has a cross-sectional width w between about 2 mm and about 8 mm and a cross-sectional length l between about 6 mm and about 15 mm. In certain cases, lateral layers 112 and 112′ have a cross-sectional width w between about 2 mm and about 7 mm and a cross-sectional length l between about 3 mm and about 12 mm. Layers 110, 112, and 112′ of multi-layer composite 106 may be different or substantially the same with respect to composition, color, and dimension (e.g., inner diameter, outer diameter, cross-sectional length, and cross-sectional width).

To reduce the contact area of the wheel 100 on a skating surface, a skater can position the bearing axis a substantially parallel to the skating surface to align force on wheel 100 with medial layer 110. The direction of force on the wheel during skating in this position is indicated by the arrow at 0° aligned with center line c. In this position, medial layer 110 of the multi-layer composite is substantially perpendicular to the skating surface, allowing lower rolling resistance and thus higher skating speed. To increase wheel contact with the skating surface, the bearing axis a can be angled (e.g., up to about) 30° in either direction with respect to the skating surface. The direction of force on the wheel during skating at angles of 30° is illustrated by arrows perpendicular to the outer surface along an edge of tire material 108, directed toward lateral layers 112, 112′. When the wheel is angled up to 30° during accelerating, cornering, or stopping, lateral layers 112, 112′ of the multi-layer composite contribute to a higher compression strain, such that the wheel deforms more under the weight of the skater to form a larger contact area between the wheel and the skating surface. The larger contact area provides improved grip for acceleration, cornering, and stopping. When the hardness or compression modulus of the medial layer 110 exceeds the hardness or compression modulus of the lateral layers 112, 112′, the percentage compression of lateral layers 112, 112′ exceeds the percentage compression of the medial layer 110.

Lateral layers of a multi-layer composite may differ in inner diameter, outer diameter, or thickness (e.g., cross-sectional width and/or cross-sectional length). Lateral layers of a multi-layer composite may also differ in hardness or compression modulus. The compression modulus gradient of wheel 100 along the bearing axis a may be symmetrical or asymmetrical about center line c of the wheel. FIG. 3 illustrates a cross section of a skate wheel 100 with multi-layer composite 106 having lateral layers 112, 112′ with a different length, width, and compression modulus. Lateral layers that differ in size, shape, or composition may be selected to achieve a desired effect on skating performance (e.g., acceleration, stopping, or breaking) based on position of the wheel on the skate (e.g., front or back), orientation of the wheel with respect to the body (e.g., left or right foot, facing outward or toward the midline of the body), degree of acceleration or deceleration, skating style of a skater, and the like.

In some cases, multi-layer composites include more than three layers. For example, a multi-layer composite with an odd number of layers (e.g., three, five, seven, nine) can include a medial layer arranged between a number of lateral layers on each side. A multi-layer composite with an even number of layers (e.g., four, six, eight) can include two medial layers be arranged between a number of lateral layers on each side. The number of lateral layers on each side of the medial layer (or layers) may be the same or different. That is, there may be more lateral layers on one side of the medial layer (or layers) than on the other side.

FIG. 4 shows a cross-sectional view of a skate wheel 100 with an even number of layers in multi-layer composite 106. Medial layers 110 and 110′ may be different or substantially the same with respect to dimension, composition, and color. Lateral layers 112 and 112′ may be different or substantially the same with respect to dimension, composition, and color. Medial layer 110 and/or 110′ can have the same dimension, composition, or color as lateral layers 112 and 112′.

FIGS. 5A-5F and 6A-6F show partial cross-sectional views of multi-layer skate wheels 100 with multi-layer composite 106, hub 104, and tire material 108. In FIGS. 5A-5F, multi-layer composite 106 is partially surrounded by tire material 108 such that at least a portion of the multi-layer composite contacts or is fixed to hub 104, and at least a portion of the tire material contacts or is fixed to the hub. In FIGS. 6A-6F, multi-layer composite 106 is surrounded (e.g., entirely surrounded or encapsulated) by tire material 108 such that multi-layer composite does not contact the hub, with the tire material separating the multi-layer composite from the hub (e.g., acting as a spacer between the hub and the multi-layer composite). That is, the inner diameter of each layer of the multi-layer composite 106 exceeds the outer diameter of the hub 104.

FIGS. 5A-5C and 6A-6C show portions of wheels 100 having three-layer composites, with medial layer 110 adjacent (or between) lateral layers 112 and 112′. FIGS. 5D-5F and 6D-6F show wheels with five-layer composites, with medial layer 110 adjacent (or between) lateral layers 112 and 112′, and lateral layers 112 and 112′ adjacent (or between) lateral layers 114 and 114′.

Multi-layer composites 106 can be formed with a variety of cross-sectional profiles. For example, FIGS. 5A and 5D show multi-layer composites 106 with a curved surface from lateral layer 112 to lateral layer 112′ and a curved surface from lateral layer 114 to lateral layer 114′, respectively. FIGS. 5B and 5E show multi-layer composites 106 with stepped surfaces from lateral layer 112 to lateral layer 112′ and stepped surfaces from lateral layer 114 to lateral layer 114′, respectively, such that medial layer 110 has a larger outer diameter than the lateral layers 112, 112′ and 114, 114′. FIGS. 5C and 5F show multi-layer composites 106 with a flat surface (e.g., substantially parallel to bearing axis a) from lateral layer 112 to lateral layer 112′ and a flat surface from lateral layer 114 to lateral layer 114′, respectively, such that medial layer 110 and lateral layers 112, 112′ and 114, 114′ have substantially the same outer diameter.

FIGS. 6A-6F also show multi-layer composites with a variety of cross-sectional profiles, with an appearance, for example, of irregular rings or multiple composition O-rings. In FIGS. 6A and 6D, the cross section of multi-layer composites 106 is an ellipse. FIGS. 6B and 6E show multi-layer composites 106 with stepped surfaces, such that lateral layers 112 and 112′, or 112, 112′, 114, and 114′, respectively, have smaller outer diameters and larger inner diameters than medial layer 110. In FIGS. 6C and 6F, the cross section of multi-layer composites 106 is rectangular, such that lateral layers 112 and 112′, or 112, 112′, 114, and 114′, respectively, have substantially the same inner and outer diameters as medial layer 110.

Layers 110, 112, 112′, etc. of multi-layer composite 106 are formed from high resilience materials, such as natural rubber and synthetic rubber (e.g., neoprene, urethane rubber, and the like), selected for desirable compression stress, compression strain, Bashore rebound, hardness, or a combination thereof. For example, a Bashore rebound of materials used to form multi-layer composite 106 is at least about 65%, at least about 70%, at least about 75%, or between about 65% and about 95%, between about 70% and about 95%, or between 75% and about 95%. A hardness of a medial layer of a multi-layer composite can be between about 50 Shore A and about 95 Shore A, between about 60A Shore A and about 95 Shore A, between about 75 Shore A and about 95 Shore A, or between about 80 Shore A and about 95 Shore A. A hardness of a lateral layer can be between about 40 Shore A and about 75 Shore A or between about 50 Shore A and about 70 Shore A.

A compression stress modulus of materials used to form multi-layer composite 106 can be between about 8% and about 40% at 50 psi. A hardness or compression stress modulus of a medial layer of a multi-layer composite is greater than or substantially equal to the hardness or compression stress modulus of at least one of the lateral layers and greater than, less than, or substantially equal to the hardness or compression stress modulus of tire material 108. The hardness or compression stress modulus of at least one of the lateral layers is less than or substantially equal to the hardness or compression stress modulus of one or more medial layers of the multi-layer composite and less than the hardness or compression stress modulus of the tire material. In an example, when the hardness or compression stress modulus of the medial layer(s) and the lateral layer(s) are substantially the same, the cross-section of multi-layer composite 106 may have a stepped configuration, as shown in FIGS. 5B, 5E, 6B, and 6E. In these stepped examples, the various layers of the inner ring may be formed together as one seamless piece of material having a hardness less than the hardness of the tire material. In another example, when the hardness or compression stress modulus of the medial layer(s) exceeds the hardness or compression stress modulus of the lateral layer(s), the outer diameter of the medial layer(s) and lateral layer(s) may be substantially the same, as shown in FIGS. 5C, 5F, 6C, and 6F.

For the multi-layer skate wheels described herein (e.g., for multi-layer skate wheels in which two or more of the layers of the multi-layer composite are formed from materials with a different compression modulus, or for multi-layer skate wheels in which two or more of the layers of the multi-layer composite have different dimensions), a compression modulus gradient is present along the bearing axis a of the wheel. This compression modulus gradient can be present even when the hardness of the lateral layer(s) is substantially the same as the hardness of the medial layer(s). In some cases, materials for the layers of a multi-layer composite are selected such that the compression stress modulus of the wheel decreases from the center of the wheel (e.g., from the medial layer(s) of the multi-layer composite or ring) to an outer portion of the wheel (e.g., to the outermost lateral layers of the multi-layer composite or ring).

FIGS. 7A-7D illustrate compression stress modulus gradients for multi-layer skate wheels along the bearing axis a for wheels including three-layer composites and five-layer composites. As seen in FIG. 7A, the compression stress modulus of the wheel proximate medial layer 110 of the multi-layer skate wheel exceeds the compression stress modulus of the wheel proximate layers 112 and 112′, and the compression stress modulus proximate layer 112 is substantially the same as the compression stress modulus proximate layer 112′. As seen in FIG. 7B, the compression stress modulus of the multi-layer skate wheel proximate medial layer 110 exceeds the compression stress modulus of the wheel proximate lateral layers 112 and 112′, and the compression stress modulus of the wheel proximate lateral layers 112 and 112′ exceeds the compression stress modulus of the wheel proximate lateral layers 114 and 114′, respectively. The compression stress modulus of the wheel proximate lateral layer 112 is substantially the same as the compression stress modulus of the wheel proximate lateral layer 112′, and the compression stress modulus of the wheel proximate lateral layer 114 is substantially the same as the compression stress modulus of the wheel proximate lateral layer 114′. As shown in FIG. 7C for a three-layer composite, the compression stress modulus of the wheel proximate lateral layers 112 and 112′ can be different. As shown in FIG. 7D for a five-layer composite, the compression modulus of the wheel proximate lateral layers 114 and 114′ can be different. Also, the compression stress modulus of the wheel proximate one or more layers positioned closer to center line c (e.g., proximate lateral layers 112′) may be less than the compression stress modulus of the wheel proximate layers positioned farther from center line c (e.g., proximate lateral layers 114 and 114′).

Ring-shaped multi-layer composites with high resilience designed for multi-layer skate wheels with a compression modulus gradient may be formed by a number of processes. Natural rubber materials can be processed by compression molding, transfer molding, injection molding, extrusion, and the like, to form layers of a multi-layer composite. Urethane layers of a multi-layer composite can be formed in a liquid phase casting process, a liquid injection molding process, or the like.

In one method, a multi-layer sheet is formed and multi-layer composite rings are cut from the sheets by a die cutting process. The multi-layer composites can be cut in the shape of rings with the same or different inner and outer diameters. FIG. 8 shows a multi-layer sheet 120 with three layers 122, 124, and 126. Multi-layer sheet 120 may include more than three layers (e.g., four layers, five layers, six layers, seven layers, etc.). In one example, layers 122, 124, and 126 are about 5 mm thick. In other examples, one or more of layers 122, 124, and 126 may be thicker (e.g., about 8 mm) or thinner (e.g., about 2 mm). Layers 122, 124, and 126 may be of the same or different thicknesses. Layer 124 may have a compression stress modulus equal to or greater than the compression stress modulus of layers 122 and 126. In some cases, layers 122 and layer 126 may be substantially the same material and have substantially the same compression stress modulus as each other, or as layer 124.

In one method, multi-layer sheet 120 is formed by chemically bonding suitable materials together during a B-stage casting process. The materials may include, for example, high rebound rubber having a Bashore rebound higher than 65% (e.g., between about 65% and about 90%, or between about 70% and about 90%). Multi-layer sheet 120 may be formed by pouring liquid-phase urethane precursors (e.g., urethane prepolymer, extender, and higher molecular weight polyol and polyamine) into a mold to form layer 122. The mold may be positioned on a heat press heated, for example, to about 240° F. When the material of layer 122 reaches a high viscosity or is partially cured (e.g., “B-stage”), a second layer of urethane precursor is poured on top of layer 122 to form layer 124. Chemical bonds are formed between layers 122 and 124 during curing to form a laminate. Bonding of layer 122 to 124 may include covalent bonding of components in layer 122 to components in layer 124. When the material of layer 124 is partially cured (“B-stage”), a third castable urethane precursor is poured on top of layer 124 to form layer 126. Layers 124 and 126 chemically bond during curing to form multi-layer sheet 120. Bonding of layer 124 to 126 may include covalent bonding of components in layer 124 to components in layer 126.

After layers 122, 124, and 126 are bonded and at least partially cured, multi-layer sheet 120 can be demolded and cooled to room temperature. Multi-layer sheet 120 may be allowed to cure at room temperature for one to three weeks to reach the desired resilience, as well as the desired physical and mechanical strength. A die cutting process can be used to cut multi-layer composites 106 with a uniform inner and outer diameter from multi-layer sheet 120. A multi-layer composite 106 formed by die cutting multi-layer sheet 120 is shown in FIG. 9.

Multi-layer sheets 120 and ring-shaped multi-layer composites 106 may be formed by other methods. For example, in some cases, a multi-layer sheet 120 is formed by using a suitable adhesive to bond pre-formed layers together, and the multi-layer sheet is die cut to yield multi-layer composites 106. In certain cases, for example when layers of a multi-layer composite have different dimensions, rings are individually cut from one or more different sheet materials, or produced separately as a tube, and then sliced to form rings. The rings are then bonded together with an adhesive to form ring-shaped multi-layer composites 106. In an example, a number of rings made of natural rubber, neoprene, or urethane rubber may be cut to size and adhered together with an adhesive to form a ring-shaped multi-layer composite ring. Examples of suitable adhesives include LOCTITE 401 and LOCTITE 420 (Henkel A G and Co., Germany).

To compound a multi-layer skate wheel, a multi-layer composite ring formed by methods described herein is placed proximate a hub (e.g., with at least portion of the inner diameter of the multi-layer composite contacting the hub or positioned about the hub with a space, for example, in the form of a spacing rim of tire material or other material between the hub and the ring-shaped multi-layer composite. The hub and ring-shaped multi-layer composite are then positioned in a wheel mold. Urethane precursors used to form the tire material are poured into the mold to at least partially surround or encapsulate the multi-layer composite ring in an over molding process, such that at least a portion of tire material is in contact with an outer diameter of the hub. After the tire material is partially cured (e.g., at least about 60-80% cured), the wheel is removed from the mold. The demolded wheel may be further processed to yield a desired size or shape.

In another method of forming multi-layer composites for skate wheels, the medial layer may be formed before the lateral layers in an open casting molding process. FIG. 10A illustrates an example of a mold 128 with core 130 and partitions 132 that can be used to form multi-layer composites in an open casting molding process. In some cases, core 130 and the interior cavity of mold 128 are substantially uniform along a length of core 130, resulting in formation of uniform ring-shaped multi-layer composites, with each layer of each multi-layer composite having substantially the same inner diameter and outer diameter. In other cases, core 130 and/or the interior cavity of mold 130 are non-uniform along a length of core 130 (e.g., the diameter of core 130 may be different along a length of the core), resulting in formation of ring-shaped multi-layer composites 106 with layers having different inner and/or outer diameters. Core 130 and partitions 132 may be made of material that does not bond with the curable compositions used to form layers of a multi-layer composite. For example, core 130 and partitions 132 may include TEFLON, VITON, TEFLON-coated metal, or the like.

Mold 128 can be used to form multi-layer composites 106 in a process that allows chemical bonding (e.g., covalent bonding) between adjacent layers in the mold. In some cases, a first curable precursor for medial layer 110 is poured between separators 132 into compartments 134 along a length of the mold. After the precursor for inner layer 110 is at least partially cured (e.g., “B-stage”), separators 132 are removed from mold 128. After separators 132 are removed, a second curable precursor for outer layers 112, 112′ is poured in compartments 136, chemically bonding with inner layer 110 during at least partial curing of the outer layers. If layers 112 and 112′ are to be formed of different materials, a second curable precursor may be poured in every other compartment 136, and a third curable precursor may be poured in the remaining compartments. After layers 112 and 112′ are at least partially cured, the composite is demolded.

Core 130 can be removed from the multi-layer composite to yield a composite tube 138, as shown in FIG. 10B, with an inner diameter substantially the same as the outer diameter of the core. Tube 138 can be post-cured in an oven between about 180° F. and about 220° F. for a length of time between about 8 hours and about 16 hours, or allowed to post-cure at room temperature for a length of time between about 3 days and about 14 days. Tube 138 can then be ground to a desired shape and size to achieve a desired profile for ring-shaped composites (e.g., as shown in FIGS. 5A-5F and 6A-6F) to be sliced from the tube. In certain cases, core 130 is removed after post-curing and grinding of tube 138. With core 130 removed, tube 138 is then sliced (e.g., proximate the centers of compartments 136) to separate layer 112 of a first multi-layer composite from layer 112′ of a second multi-layer composite. In some cases, e.g., for forming ring-shaped multi-layer composites with a varying outer diameter, tube 138 is turned inside-out, subjected to grinding at selected regions along the tube, and then turned outside-in to achieve a desired profile of the inner diameter of the ring (e.g., as shown in FIGS. 5A-5F and 6A-6F).

As shown in FIG. 10A, partitions 134 are used to achieve a desired width w, as shown in FIG. 2, of medial layer(s) of the multi-layer composite. In other cases, i.e., for multi-layer composites with more than three layers, or for multi-layer composites with lateral layers formed of different materials, additional partitions may be used. That is, additional partitions may be used to separate adjacent lateral layers from each other. An over molding process as described herein may be used to encapsulate or at least partially surround the multi-layer composite with tire material to form a solid core skate wheel.

Precursors used to form urethane rubber suitable for the multi-layer composite rings include diisocyantes, curatives, and additives. The diisocyanates include very high NCO isocyanates (NCO>20) (e.g., for a one-shot process) and high NCO prepolymers (NCO>9). The isocyanate backbones can include methylene diisocyanate (MDI), para-phenyl diisocyanate (PPDI), toluene diisocyanate (TDI), naphthalene diisocyanate(NDI) (e.g., available from Bayer Material Science, Pittsburgh, Pa.), or a combination thereof, prepolymerized with one or more ether-based and/or ester-based polyols or polyamines. The curatives include a combination of lower molecular weight diols (e.g., from GAF Chemical Corporation, Wayne, N.J.) or diamines (e.g., from Air Products, Allentown, Pa.), extenders and higher molecular weight polyols (e.g., from E I Dupont, Wilmington, Del.) and polyamines. Suitable lower molecular weight diol extenders include, for example, hexadiene diol, pentadiene diol, butadiene diol, and propylene diol (e.g., from Sigma-Aldrich, Inc., Atlanta, Ga.). Suitable lower molecular weight diamine extenders include, for example, ETHACURE-100, ETHACURE-300, and LONZACURE, methylene-bis-orthochloro aniline (MOCA) (e.g., from Sartomer, Exton, Pa.). Suitable higher molecular weight polyols and polyamines include, for example, poly(tetramethylene)diol (PTMEG) with a molecular weight higher than 1000 (e.g., 1000-3000), such as PTMEG 1000, PTMEG 1500, PTMEG 2000, PTMEG 2900, PTMEG 3000, polycaprolactone, CAPA 720 (e.g., from E. I. DuPont), VERSALINK P-1000, VERSALINK P-2000, and VERSALINK 3000 (e.g., from Air Products). Additives can include, but are not limited to, one or more catalysts, stabilizers (e.g., UV stabilizers), antioxidants, and colorants. Suitable catalysts include, for example, DABCO 33LV, DABCO T-12, T-9 (e.g., from Air Products), and FOAMEX UL-29, and FOAMEX UL-32 (e.g., from Witco, Taft, La.). Suitable UV stabilizers include, for example, TINAVIN 328, TINAVIN 783FB, and TINAVIN 213 (e.g., from CIBA, Tarrytown, N.Y.). Suitable antioxidants include, for example, BHT, IRGANOX 245, IRGANOX 1076, IRGANOX 1135 (e.g., from CIBA).

EXAMPLES

High resilience urethane rubber samples A-E were prepared as described below. ASTM Test Methods include Method D2240 for hardness, Method 412 for tensile modulus and elongation modulus, Method D624 for tear strength, and Method D575 for compression modulus.

Sample A. A metering machine (e.g., from Max Machinery Inc., Healdsburg, Calif.) having three streams was used to pour urethane precursor materials into an aluminum or stainless steel tube mold with various center cores. The mold was heated to 240° F. and positioned on top of a rotational round table. 38.77 parts PAPI 2094 at 90° F., 385.83 parts PTMEG 2900 at 160° F., and 25.40 parts of a mixture with polyol, color, and catalyst at a 3000:390:3.6 w/w/w ratio, respectively, at 140° F., were metered into the tube mold with a total flow rate of 450 grams per minute After metering the liquid precursors into the tube mold and curing in the mold for 3-10 minutes, the urethane tube was demolded and post-cured at room temperature for 8-12 hours, yielding a light brown translucent solid. The tube was then ground to the specified outer diameter to yield cross-sectional length l of about 6 mm and sliced into rings with a thickness (or width w, as shown in FIG. 2) of about 3 mm to form rings for the lateral layers of multi-ring composites. Another tube of the same material was ground to the specified outer diameter to yield cross-sectional length l of about 12 mm and sliced into rings with a thickness or width w, as shown in FIG. 2, of about 5 mm to form rings for the medial layer of multi-ring composites. Two lateral rings were bonded to opposite sides of a medial ring with LOCTITE 420 adhesive. The Bashore rebound for an ASTM button (1″×1″×½″ cube) from Sample A material was 85%, and the hardness was 62 Shore A.

Sample B. Sample B was prepared in a manner similar to that of Sample A, with a total flow rate of 450 grams per minute. The precursors included 34.05 parts PAPI 2094 at 90° F., 215.06 parts ACCLAIM 4220N at 160° F., 182.91 parts of T-2900 at 160° F., and 17.97 parts of a curative mixture at 140° F., the curative mixture including 3000 parts T2900, 390 parts dye, Reactint X64 red (from Milliken, Spartanburg, S.C.) and 3.60 parts UL-32. After metering the material into the tube mold, the tube was demolded and continuously cured at room temperature for 8-12 hours, yielding a cloudy solid material. The tube was then ground to the specified outer diameter and sliced into rings with cross-sectional dimensions of 4-12 mm in length (l) and 3-10 mm in width (w), as illustrated in FIG. 2 for various inner diameters. The Bashore rebound for an ASTM button from Sample B material was 76%, and the hardness was 54 Shore A.

Sample C. Sample C was prepared in a manner similar to that of Sample A, with a total flow rate of 450 grams per minute. The precursors included 173.3 parts of Bayer ME-120 at 150° F., 11.1 parts propanediol at 90° F., and 265.6 parts of a curative mixture at 150° F., the curative mixture including 100 parts PTMEG 2900, 1.5 parts of UV stabilizer T328, 0.75 parts BHT, and 0.02 parts UL-29. After metering into an aluminum or steel tube mold, the urethane tube was demolded and then post-cured for 8 to 12 hours at room temperature, yielding a clear solid. The tube was then ground to the specified outer diameter and sliced into rings with cross-sectional dimensions of 6 to 12 mm in length (l) and 3 to 8 mm in width (w), as illustrated in FIG. 2 for various inner diameters. The Bashore rebound for an ASTM button from Sample C material was 78%, and the hardness was 68 Shore A.

Sample D. Sample D was prepared in a manner similar to that of Sample A, with a total flow rate of 500 grams per minute. The precursors included 471.6 parts of Dow ISO NB1701191-3 at 176° F. and 28.4 parts of DOW Polyol NB1701052 at 90° F. After metering into an aluminum or steel tube mold, the urethane tube was demolded and then post-cured for at least 3 days at room temperature, yielding a clear solid. The tube was further ground to specified outer diameter and sliced into rings with cross-sectional dimensions of 6 to 12 mm in length (l) and a width of 3 to 10 mm (w) as illustrated in FIG. 2 for various inner diameters. The Bashore rebound for an ASTM button from Sample D material was 75%, and the hardness was 79 Shore A.

Sample E. Sample E was prepared in a manner similar to that of Sample A, with a total flow rate of 450 grams per minute. 413.9 grams of resin (Chemtura LFX035), 26.0 grams of a first curative (including Ethacure 100 and PTMEG polyol), and a second curative including 100 parts A272 (a 1:1 mixture of PTMEG 1000/PTMEG 2000 by weight), 1.5 parts of T328, 0.75 parts of BHT, and 0.049 parts of Ul-29 were metered into the tube mold. After curing in the mold for 3-10 minutes, the urethane tube was demolded and post-cured at room temperature for 8-16 hours, yielding a clear solid. After post-curing, the tube was ground to the specified outer diameter and sliced into rings with cross-sectional dimensions of 6-12 mm in length (l) and 3-10 mm in width (w), as illustrated in FIG. 2. The Bashore rebound for an ASTM button from Sample E material has a Bashore rebound of 76%, and a hardness of 88 Shore A.

Sample F. Sample F was prepared in a manner similar to that of Sample A, with a total flow rate of 500 grams per minute. The precursors included 255.4 parts of Bayer ME-120 at 165° F., 20.3 parts propanediol at 90° F., and 224.3 parts PTMEG 2900/DABCO at 170° F., where PTMEG 2900/DABCO is a mixture of 100 parts of PTMEG and 0.9 parts of DABCO 33LV. After metering into an aluminum or steel tube mold, the urethane tube was demolded and then post-cured for at least 3 days at room temperature, yielding a milk-white solid. The tube was further ground to the specified outer diameter and sliced into rings with cross-sectional dimensions of 6 to 12 mm in length (l) and 3 to 10 mm in width (w) for various inner diameters. The Bashore rebound for an ASTM button of Sample F material was 75%, and the hardness was 84 Shore A.

Table I lists the durometer, Bashore rebound, tensile strength, % elongation at break, and Die C tear, for urethane rubber samples A-E. Samples A-C, with a Bashore rebound greater than about 75% and a hardness of 62 Shore A, 54 Shore A, and 68 Shore A, respectively, are suitable for use as lateral layer materials for multi-layer composites. Samples D and E, with a Bashore rebound greater than about 70% and a hardness of 79 Shore A and 88 Shore A, respectively, are suitable for use as medial layer materials for multi-layer composites. In some cases, as described with respect to Sample A above, the dimensions of a ring of a multi-layer composite can be selected such that the same material is used to form medial as well as lateral layers of a multi-layer composite. For example, as described with respect to Sample A, the lateral rings can have a smaller outside diameter or smaller cross-sectional length l than the medial ring(s) to achieve a desired compression modulus gradient, with the hardness of the tire material exceeding the hardness of the lateral layer(s).

TABLE I Physical properties of high resilience urethane rubber samples. Tensile Durometer Bashore Strength Elongation at Die C Tear Sample (Shore A) Rebound (%) (lbs/in²) break (%) (lbs/in) A 62 85 1195.9 530.0 164.6 B 54 76 398.4 213.8 168.1 C 68 78 1458.3 505.6 221.7 D 79 75 1702.7 334.2 378.7 E 88 71 1508.1 308.0 353.1

Table II lists the tensile modulus of urethane rubber samples A-E stretched from 100% to 300% of a sample's original height.

TABLE II Tensile modulus of high resilience urethane rubber samples. Tensile modulus (lbs/in²) Sample 100% 200% 300% A 288.4 392.4 529.2 B 275.1 382.5 — C 376.1 541.0 754.1 D 721.8 1093.8 1540.5 E 979.5 1212.1 1490.8

Table III lists the compression modulus for urethane rubber samples A-E at deformations ranging from 3% to 50% of a sample's original height for a known load.

TABLE III Compression modulus of high resilience urethane rubber samples. Compression modulus (lbs/in²) Sample 3% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% A 7.37 12.2 24.5 36.5 48.1 59.6 71.0 82.5 93.5 104.3 114.7 B 5.7 9.5 19 28.3 37.4 46.3 55.2 63.3 71.9 80.6 89.0 C 8.4 13.5 26.9 40.1 53 65.5 77.9 90.4 90.4 114.2 125.8 D 16.1 26.5 52.9 77.9 100.8 122.2 142.2 163.5 163.5 201.5 220.0 E 30.6 50.4 91.7 123.4 140.7 175.6 198.9 223.2 223.2 266.1 286.6

FIG. 11 shows plots of compression modulus data in Table III as stress vs. percent strain. Plots 140, 142, 144, 146, and 148 show the compression modulus of Samples A-E, respectively, over a range of 0% to 50% strain. Samples A-C, which are suitable at least for use as lateral layers of a multi-layer composite, show a much lower compression modulus than Samples D and E, which are suitable at least for medial layer materials of a multi-layer composite. As seen in FIG. 11, when the stress or compression is 50 psi, Sample B (durometer 54 Shore A) exhibits strain of about 28%, and Sample E (durometer 88 Shore A) exhibits strain of about 5%. Thus, at this level of stress, Sample B (an example of a softer lateral layer material for a multi-layer composites) is about 6 times more compressible than Sample E (an example of a harder medial layer for multi-layer composites). When the stress or compression is 75 psi, Sample B exhibits strain of about 40%, and Sample E exhibits strain of about 7%. At this increased level of stress, Sample B is also about 6 times more compressible than Sample E.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. 

1. A wheel comprising: a hub defining a bearing axis; and a tire mounted about the hub, the tire comprising: an inner ring; and an outer tire material disposed about the inner ring and forming a rolling surface of the wheel, wherein: the outer tire material is harder than the inner ring; and the inner ring has a stepped profile in cross section, defining a middle portion disposed axially between lateral portions of the inner ring, with the middle portion having a greater outer diameter than the lateral portions.
 2. The wheel of claim 1, wherein the Bashore rebound of the inner ring is at least about 65%.
 3. The wheel of claim 1, wherein the inner ring extends a distance of between about 6 mm and about 15 mm from the hub.
 4. The wheel of claim 1, wherein the tire material has a hardness of between about 70 Shore A and about 95 Shore A.
 5. The wheel of claim 1, wherein the profile of the inner ring defines a single step on either side of the middle portion.
 6. The wheel of claim 1, wherein the inner ring has a compression stress between about 35 psi and about 160 psi when under a compression strain of 20%.
 7. The wheel of claim 1, wherein the wheel has a compression modulus gradient in which the compression modulus of the wheel varies along the bearing axis in accordance with the stepped profile of the inner ring.
 8. The wheel of claim 1, wherein the inner ring has a hardnes between about 40 Shore A and about 75 Shore A.
 9. The wheel of claim 1, wherein the wheel is an in-line skate wheel.
 10. The wheel of claim 1, wherein the inner ring is formed by thermoset urethane casting of urethane precursors comprising one or more components selected from the group consisting of MDI, , TDI, PPDI; PTMEG with a molecular weight between about 1000 and about 3000: polycliol or polyamine, and butadiene diol, propylene diol, pentane diol, and hexanediol with a molecular weight between about 40 and about
 80. 11. The wheel of claim 1, wherein the tire material contacts the hub.
 12. A method of making a solid core skate wheel, the method comprising; providing a hub assembly comprising an inner ring having a stepped profile in cross section disposed about a wheel hub, defining a middle portion disposed axially between lateral portions of the inner ring, with the middle portion having a greater outer diameter than the lateral portions; and over molding the inner ring with a tire material forming a roiling surface of the wheel, such that the inner ring is encapsulated of at least partially surrounded by the tire material and the tire material is fixed to the hub assembly, thereby forming a tire from the tire material having a hardness greater than the hardness of the inner ring.
 13. The method of claim 12, wherein the inner ring contacts the hub.
 14. The method of claim 12, wherein the inner ring forms a seamless mass of resin.
 15. The wheel of claim 1, wherein the lateral portions of the inner ring extend a distance of between about 2 mm and about 12 mm from the hub.
 16. The wheel of claim 1, wherein the inner ring has a compression strain between about 5% and about 50% when under a compression stress of 75 psi.
 17. The wheel of claim 1, wherein the inner ring contacts the hub.
 18. A wheel comprising: a hub defining a bearing axis; a solid core tire comprising: a tire material fixed to the hub; and a multi-layer composite coaxial with the bearing axis, the multi layer composite forming a ring around the hub and at least partially surrounded by the tire material, wherein: the multi-layer composite comprises a medial layer and at least two lateral layers adjacent to the medial layer, a hardness a the medial layer of the inalti-layer composite is equal to or greater than a hardness of at least one of the lateral layers of the multi-layer composite, and a hardness of the tire material is greater than the hardness of at least one of the lateral layers, and an outer diameter of the multi-layer composite is less than or equal to an outer diameter of the tire material. 